1. Field of the Invention
The present invention relates generally to circuit breakers and more particularly, to an opening/closing operation mechanism for a circuit breaker.
2. Description of the Background Art
A conventional circuit breaker is disclosed by Japanese Patent Laying-Open No. 61-39427 and a main part of the circuit breaker will be now described in conjunction with FIGS. 9 to 11.
A contact portion including the conduction portion of a main circuit in this circuit breaker is formed on a mold base 100, and the circuit breaker includes a stationary contact 101 also serving as a power supply side terminal, a load side terminal 102, a movable contact 103 which contacts/separates from stationary contact 101, and a flexible lead conductor 104 which connects the movable contact and the load side terminal. Movable contact 103 is pivotably supported by a movable contact holder 106 through a shaft 105. A contact pressure spring 107 is provided between movable contact 103 and movable contact holder 106 to apply contact pressure between both contacts, and movable contact holder 106 is pivotably supported by a fixed member through a shaft 108 and coupled with an insulating rod 109, which is operated by an opening/closing mechanism portion such that both contacts contact and separate as will be described.
A toggle link mechanism is employed for the opening/closing mechanism portion, and a closing link 110, a trip link 111, and a trip bar 112 in this order from an end of insulating rod 109 are coupled rotatably with one another through shafts 113, 114 and 115, respectively. Insulating rod 109 is further coupled to a connector lever 117 secured to a cross bar 116 through shaft 113, and a breaking spring 118 having one end attached to shaft 113 biases movable contact holder 106 anti-clockwise and connector lever 117 clockwise. Note that a trip mechanism coupled with trip lever 112 is not directly related to the present invention and therefore is not described.
The operation of the circuit breaker will be now described.
In this circuit breaker in a closed state as shown in FIG. 9, closing link 110 and trip link 111 are biased to bend into a dogleg shape at shaft 114, a coupling portion, by the rotational force of connector lever 117 by the force of breaking spring 118 and contact pressure spring 107, but they are held in an extended state due to engagement of one end of a closing latch 120 and a closing roller 119 provided at shaft 114.
When a tripping instruction is given in this closed state, though not detailed, trip lever 112 rotates clockwise, trip link 111 and closing link 110 move downward, connector lever 117 rotates clockwise, and movable contact holder 106 rotates anti-clockwise so that both contacts separate in a trip state as shown in FIG. 10. At this time, a closing roller 119 is detached from closing latch 120 and moves along the outer circumference of a closing cam 121 which will be described.
The circuit breaker is a spring closing type closed by operating a opening/closing mechanism by releasing a closing spring (not shown) charged by an electric motor or the like, and in a trip state, when the force of the spring is charged, closing cam 121 rotates anti-clockwise in the process, closing cam 121 is biased anti-clockwise when the charging of force completes, a holding roller 122 attached to closing cam 121 engages with a release lever 123, and a reset state as shown in FIG. 11 is attained. At this time, closing roller 119 comes into a position opposite to the edge recess portion 121a of closing cam 121, and trip lever 112 rotates anti-clockwise to regain the original position.
In the closing operation of this circuit breaker, as release lever 123 rotates anti-clockwise in response to a closing instruction and is disengaged from holding roller 122, and large closing force stored in the closing spring causes closing cam 121 to rapidly rotate anti-clockwise, and the outer circumference of closing cam 121 whose position comes away from the center of rotation as the rotation continues pushes closing roller 119 to the right, which causes closing link 110 and trip link 111 to be extended. This extension causes connector lever 117 to rotate anti-clockwise through shaft 113 and movable contact holder 106 to rotate clockwise such that the closed state shown in FIG. 9 is attained.
This circuit breaker must maintain insulation performance when the contacts are in an open state such as in a trip state and a reset state, and therefore stationary contact 101 and movable contact 103 are apart from each other with a relatively large insulation distance. Movable contact 103 rotates clockwise by a rotation angle corresponding to this relatively large insulation distance until contacting. During the rotation, only the closing force against breaking spring 118 is necessary. After both contacts make contact, movable contact 103 remains at the position and movable contact holder 106 further rotates slightly in the clockwise direction. The further rotation after the contacting could be described as that movable contact 103 is pressed into stationary contact 101, and the amount of the further rotation is very small in comparison to the amount of rotation since movable contact 103 starts rotating until both contacts make contact. The amount of the further rotation is necessary for securing conduction of current if the contacts wear.
Meanwhile, a spring having a large acting force is selected for contact pressure spring 107 because large contact pressure is necessary between both contacts to stably passing a rated current or resist a large short circuit current. As a result, large closing force enough to resist breaking spring 118 and contact pressure spring 107 is necessary in the rotation after the contacting.
More specifically, in the opening/closing mechanism for the circuit breaker, the rotation angle until the movable contact contacts the stationary contact is large while the closing force may be small until contact, and the rotation angle may be small while the closing force must be large enough to resist breaking spring 118 and contact pressure spring 107 in the rotation after the contacting.
Simply using a closing spring generating closing force larger than necessary for the circuit breaker is however not desirable. This is because the use of such a spring increases the size of the circuit breaker, the other elements must be also strong enough to resist the closing force, and the mechanical stress increases as a result, which is not desirable in terms of the useful life of the circuit breaker.
In this conventional circuit breaker, the cam surface of closing cam 121 is formed to have such a shape that closing link 110 and trip link 111 are greatly extended in the initial step of releasing the closing spring until both contacts come into contact and after both contacts are in contact and until the completion of closing, a large part of the closing force of the closing spring is used to slightly extend the links for the purpose of solving the above-described problem as well as satisfying the required closing characteristic.
The closing force of the conventional circuit breaker cannot be precisely controlled since the circuit breaker uses only a set of cam means (closing cam 121 and closing roller 119), and the cam means are provided at coupling shaft 114 between closing link 110 and trip link 111 through a number of elements from the contacting position of both contacts, so that a larger closing spring with larger allowance should be prepared in view of variation in the size of the parts.
Furthermore, the contact portion and the opening/closing mechanism portion must be combined for example through insulating rod 109, connector lever 117, closing link 110 and shaft 113, which makes assembling complicated.